Electrical apparatus housing with interlock for removable units



Aug. 4, 1970 FRADLEY, ETAL 3,523,218

ELECTRICAL APPARATUS HOUSING WITH INTERLOCK FOR REMOVABLE UNITS Filed Aug. 26, 1968 3 Sheets-Sheet 1 Aug. 4, 1970 FRADLEY ET AL 3,523,218

ELECTRICAL APIARATUS HOUSING WITH IRTERLOCK FOR REIOVABLE UNITS I Filed Aug". 26, -1J68' FIG.3

111 11 111111 1111111111111 IHITIIIIIIIIIIIIIIIIIIIIIIIIIJII United States Patent "ice 3,523,218 ELECTRICAL APPARATUS HOUSING WITH INTERLOCK FOR REMOVABLE UNITS Gordon Albert Fradley and Brian David John Potts, Stalford, England, assignors to The English Electric Company Limited, London, England, a British company Filed Aug. 26, 1968, Ser. No. 755,147

Claims priority, application Great Britain, Aug. 24, 1967,

Int. Cl. H02b 1/02 U.S. Cl. 317120 12 Claims ABSTRACT OF THE DISCLOSURE This invention provides a housing for static relay equipment arranged on a modular basis. The housing contains a connector module associated with a group of operational modules, with a bridging plug for use with the connector to connect the supply to the remaining group. The bridging plug is so arranged that these connections are effected in a particular sequence, and interlock facilities are available whereby none of the modules may be removed without the connector module having first been removed.

This invention relates to housings for electrical apparatus and particularly, but not exclusively, relates to housings for protective relay schemes.

From one aspect, the present invention provides a housing for electrical apparatus, comprising a frame having laterally spaced guide members for accommodating between them a plurality of modular units containing the said apparatus, a connector module having one bank of conductors connected to exterior terminals on the housing and another juxtaposed bank connected to one or more of the modular units, a bridging plug for connecting together the two banks of conductors, said conductors and/or the bridging connection on the plug being staggered in a manner such that one group of associated condoctors in the banks is disconnected before the other on removal of the plug and conversely the said other group is interconnected before the one group on insertion, and a locking bar operable to release the modular units for removal only following the removal of said plug.

Preferably, the bridging plug comprises first and second separable. portions associated with the said one and said other groups of conductors, respectively, the two plug portions being interconnected so that whereas the first portion may be removed alone the second plug cannot be removed without the first, the locking bar then being operable in the manner described only following the removal of the second plug portion.

A master interlock feature may be incorporated, particularly where more than one set of modules together with their connector modules are mounted in close proximity to one another or even in juxtaposition within the same frame, this interlock conveniently being in the form of a plunger effective on the said first plug portion in the or each connector module so as to prevent its unauthorised removal. This feature is of particular importance since in view of the increasing tendency to offer protective equipment in electronic form it is therefore becoming smaller and it is often no longer economic to have the mechanical segregation between different units demanded in the past where one or more of the units is to be made inoperable and, for example, routine testing carried out in close proximity to the live units. By providing this master interlock feature however, it is possible to isolate any selected unit whilst maintaining the interlock on the other unit(s) thus preventing its unauthorised or accidental removal.

3,523,218 Patented Aug. 4, 1970 particular housing but their width may vary in accordance with various multiples of a standard width; in this respect the connector module may be of standard width.

The connections from the bank of conductors to the modular units and the connections between these units themselves may be effected through contact block mouldings upstanding at the. rear of the frame and adapted to receive plug connectors from component boards, e.g., printed circuit boards, of the modular units.

As mentioned above, the action of insertion and withdrawal of the bridging plug or plug portions in the connector dictates a specified sequence of connections. In particular, when the housing is designed for protective relay schemes it is frequently necessary to provide circuitbreaker trip circuits and provide monitoring facilities for electrical parameters, e.g., voltage and current, of the protected system. The first plug portion may be associated with the trip circuits and the second plug portion associated with the monitoring facilities so that, by reason of their mutual interlocking feature and the staggered connections, the trip circuits must be isolated by removal of the first plug portion if the second is removed. Again, the monitoring facilities may include current transformers and in order to avoid open-circui t ing the secondary windings these windings may be shortcircuited whenever the second plug portion is removed, the arrangement being such that the short circuit is applied before the bridging contacts are opened and, conve'rsely, the bridging contacts are made on insertion before the short-circuit is broken.

The housings may themselves be stacked one upon the other in a rack assembly in order together to provide a flush-mounted cabinet housing a complete relay scheme. Housings in accordance with this invention thus provide a compact assembly of a multiplicity of different modular units which are all dimensioned in a specified relationship so as to provide an easy interchange of modules. All the wiring between the modules is contained internally within the housings thus mitigating problems of external interference, stray capacitance and simplifying screening, and the interlock features simplify and safeguard the checking and maintenance routines.

In order that the invention may be fully understood, one embodiment thereof will now be described 'with reference to the accompanying drawings, in which:

FIG. 1 illustrates front elevation of the housing, with parts broken away, and the front cover removed;

FIG. 2 illustrates a sectional side elevation along AA in FIG. 1; and

FIG. 3 illustrates a sectional plan view along BB in FIG. 1.

Referring now collectively to the drawings, the housing comprises four extruded crossbars 1 to 4 which are secured between two flanged side plates 5, 6. These two plates are secured at their rear ends to a backing plate 8 carrying a number of terminal studs 9, and upper and lower cover plates 10, 11 are secured to the assembly by nestling in slotted recesses provided along the length of the crossbars.

Mounted within the housing are a number of modular units designed to perform different specified functions in a complete protective relaying scheme; these units are identified by the reference numerals 12, 13, 14 and 16, the modular unit between units 14 and 16 being removed to show the internal layout. In addition, a heavy duty connector for the tripping and the supply circuits is also provided, this connector including two separable plugs 18, 19 and occupying a width proportional to that of a standard module, the width of all modules being equal to, or multiples of, this standard width.

Each module has a front plate 20, which may conveniently carry potentiometers, indicator lights, etc., and has a rectangular aperture 21 adjacent its lower end for accommodating a tool by which the whole module may be removed, this plate being carried between two transverse extrusions 22, 23. In addition, the extrusion 23'has a recess 24 formed at its lower left hand corner for a purpose to be described.

Secured to the rear side of the front plate is a component board 25, and on the larger modules, e.g., module 12, a metallic support plate 26 is secured to the left hand side, tie-bars 27 extending between the board and this plate at the rear.

The rear ends of the component boards, which may be printed circuit boards, are provided with a number of connectors 29 which are so disposed as to mate with selected contact sockets 30 arranged in a stacked array in a plastics moulding 31 secured between the crossbars 3 and 4.

On the smaller modules, where metallic support plates are not provided, the component board 25 may include an earthing strip electrically connected to the front plate, this strip being positively earthed by a spring 33 secured to the lower rear crossbar 3. On larger modules, this spring makes contact with the support plate 26.

The modules are supported by, and movable along, upper and lower slotted guide plates 35, 36 which are secured between the upper crossbars and the lower crossbars, respectively, the guide surfaces defined by these plates accommodating the component boards and, on the larger modules, the support plates, and being spaced apart from one another by a distance corresponding to an integral submultiple, e.g., /2, of the standard module Width.

The heavy duty connector includes, in addition to the two plugs 18, 19, two juxtaposed contact blocks 37,- 38 'with which both plugs engage, the blocks being secured between support strips 39, 40 which lie along the upper and lower guide rail slots and are secured to a moulded pillar 41. In particular, the two blocks may either together be secured to the support strips or only the block 37 may be secured in this manner with block 38 being secured to the adjacent module. Each block carries anumber of mutually aligned fixed contact strips 42, 43-, the contacts 42 carrying the connections to the housing from the terminal studs 9 and being additionally supported by the pillar 41, and in addition the block 37 carries at selected points a shorting contact strip 44 which is T- .shaped in side elevation and biassed by a spring 46 towards the adjacent contacts 42 in this block. This contact 44 lies in a recess in the moulding intermediate those in which the contacts 42 lie and is held away from these contacts when the two plugs 18, 19 are in position.

These two plugs are mouldings and constitute bridging plugs since they serve to connect together the contact pairs 42, 43. Each plug includes a flanged finger grip 46 and carries a U-shaped bridge conductor 47 urged inwardly by a spring 48 which embraces this conductor. The inner surfaces of the moulding are designed to interleave with the like surfaces of the moulded blocks 37, 38, and in the plug 19 protruding wall portions 50 are arranged to abut the shorting contacts 44. The relative dimensions and layout of these wall portions with the contacts 42 and 44 and the bridge conductor 47 are such that on withdrawal of the plug the contact 44 is released to engage the adjacent contacts 42 before the bridge conductor 47 disengages from contacts 42 and 43 and, upon insertion, these contacts engage before the shorting contact 44 is broken. In addition, the plugs are interlocked in a manner such that the finger grip 46 on the plug 19 underlies a corresponding portion of the finger grip on the upper plug 18 so that the lower plug 19 cannot be withdrawn Without this upper plug being withdrawn also.

Further, the two plugs 18, 19 respectively engage spring-biassed catches 52, 53 mounted on the forward ends of the strips 39, 40. In particular, the side of the lower plug 19 engages the catch 53 as it is pushed home and pivots it about a screw-threaded pin 55 against the restoring action of a spring 56 which normally depresses this catch against the front face of the crossbar 2. The upper plug 18 similarly engages the catch 52 so that, when both plugs have been inserted the catches are cleared from the crossbars permitting a rectangularly framed glazed cover (not shown) to be fitted over the front of the housing and secured to the flanged side plates, whereas if either one or both plugs are not in place this cover fouls the eatch(es) and cannot be fitted.

A further interlock scheme prevents withdrawal of any one of the modules whilst the connector plugs are in situ. This interlock comprises a bar 58 which is captively held along the front of the lower crossbar 2, the interlock bar carrying a number of upstanding posts 59 corresponding to the number of modules in the housing and having a cut away portion on the front face at its left-hand end with a stop 60 provided on the protruding edge thus defined adjacent the connector plugs. With these plugs in situ the bar 58 is immovable since its stop 60 abuts the bridging plug 19, but when this plug is removed it is slidable along the crossbar to a limit determined by its extreme end 61 which then abuts the side plate 5, the disposition of the posts 59 being such that in this limiting position they lie in alignment with the recesses 24 in the module extrusions thereby enabling these modules to be freely removed.

As mentioned above, the housing may readily be designed to house protective relay equipment and in this event the large module adjacent to the connector may contain the current and voltage transformers for determining the operating parameters of the equipment with other modules containing, e.g., distance measuring units, timing units, etc. Thus, in addition to the h.t. supply po tential for all these units, the terminals 9 carry the high currents and voltages monitored from the protected system and the control currents for the circuit-breaker trips, and these are, in turn, coupled to the heavy duty connector. With such a scheme, it will be evident that any access required to the modules for inspection, adjustment, maintenance, etc., should not result in the circuit breakers being tripped and the system taken out of commission, and in order to effect this the two bridging plugs are arranged, as mentioned above, so that the plug 18, which governs these trip circuits, must be removed in the event of the removal of the plug 19 giving access to the current and voltage supplies and possible removal of the modules, removal of the plug 18 isolating the trip circuits. Furthermore, removal of the plug 19, which includes the secondary connections of current transformers associated with the system, must not result in the current transformer secondaries being left open-circuit and for this reason the shorting contact 44 is provided in the connector to short-out these secondary windings. Subsequent testing with test plugs for injecting known electrical quantities is then ineffective to upset this relationship unless the incoming supplies are to be monitored. As mentioned above, the plug 19 and the relevant contacts are so arranged as to ensure that the shorting contact is effective before the associated contact strips are broken and that, conversely, the contacts are made before the short is removed.

Although the invention has been described with reference to one particular form of housing it is to be understood that various modifications may readily be made without departing from the scope of this invention. For example, only one connector has been shown for the housing but two, or even more, may conveniently be accommodated for various sets of modules performing different functions so as to enable work to be carried out on one set without affecting the others. Further, the two plugs shown may be a single integral structure instead of being separable. In addition a master interlock in the form of a solenoid-operated plunger may conveniently be associated with each connector to prevent its unauthorised removal, this plunger being effective on the upper plug 18.

Furthermore, for complex electronic circuitry it may be unnecessary to provide in all cases a removable modular housing for each unit, and in these instances the guide plates may support rows of plain printed circuit cards which engage the contact sockets 30' at the rear but do not have front panels.

A further modification envisaged concerns the disposition of the heavy duty connector and this may be located on the right-hand side of the housing instead of the left-hand side as shown, with the stop on the interlock bar, and the catches 52, 53, being appropriately shifted. In this instance the printed circuit boards may all lie on the left hand side of their module instead of the arrangement shown where they lie on the left only in the smaller modules where the metallic support plates are not fitted.

Finally, although all the input terminal studs have been shown to be located on the backing plate these terminals may conveniently be situated instead on the side plates or even at the front of the housing if desired, deployment of the terminals in this manner however resulting in a smaller area being available for the modules.

We claim:

1. A housing for electrical apparatus, comprising a frame having a plurality of laterally spaced guide members for accommodating between them a plurality of modular units containing the said apparatus a connector module mounted on said frame having a first bank of conductors connected to exterior terminals on the housing and a second juxtaposed bank connected to internal terminals on the housing, the modular units being adapted to engage with these internal terminals a bridging plug engageable with said connector module for connecting together the two banks of conductors, said conductors and the bridging connection on the plug being staggered in a manner such that one group of associated first and second conductors in the banks is disconnected before the other group on removal of the plug and conversely the said other group of first and second associated conductors is interconnected before the one group on insertion, and a locking bar on said frame for engaging each of said modular units and said plug, said bar including means operable to release the modular units for removal only following the removal of said plug.

2. A housing according to claim 1, wherein the guide members are equidistantly spaced apart from one another, the width of all the modular units, including the connector module, being a standard dimension, or multiples of this dimension.

3. A housing according to claim 2, comprising means for separately securing the guide members to the top and to the bottom of the frame, all the members at the top and all the members at the bottom each forming part of an integral unit.

4. A housing according to claim 2, wherein the modular units each define a slot on their front face, and comprising a plurality of upstanding posts on said locking bar corresponding in number to the modular units, the

locking bar extending along the front of the frame and being movable, following the removal of the connector module, to a position in which the posts are in alignment with the slots in the modular units whereby to perm-it of their withdrawal.

5. A housing according to claim 4, comprising an extruded crossbar constituting part of the frame, the locking bar being captively held in said bar.

6. A housing according to claim 4, comprising a cover plate for engaging the front of the frame, and

pivotal catch members mounted adjacent the front of the frame and engageable by the said bridging plug, the catch members overlying the front of the frame in the absence of the bridging plug and inhibiting the closure of the cover plate until this plug is reinserted.

7. A housing according to claim 6, wherein said modular units comprise component boards having edge connectors, the housing comprising a plurality of contact block mouldings corresponding in number to the modular units and upstanding at the rear of the frame for receiving said edge plug connectors, and

means for connecting the said second bank of conductors in the connector module to the contact block mouldings.

8. A housing according to claim 7, comprising an externally controllable interlock plunger mounted on the frame and engageable with said connector module whereby to prevent its unauthorised removal.

9. A housing according to claim 4, wherein the bridging plug comprises a first separable portion associated with the said one group of conductors, and

a second separable portion associated with the said other group of conductors, the two plug portions overlapping one another so that whereas the first portion may be removed alone the second portion cannot be removed without the first,

and the housing comprises stop means on the locking bar abutting the second portion whereby the modular units may be released only following the removal of the said second portion of the plug.

10. A housing according to claim 9, comprising a plurality of sets of connector modules and their associated modular units located within a single frame.

11. A housing according to claim 10, comprising a plurality of frames and their associated modules stacked together in a rack assembly.

12. A housing according to claim 9, wherein the electrical apparatus is a protective relay, the said one group of conductors being associated with trip circuits and the said other group being associated with monitoring circuits.

References Cited UNITED STATES PATENTS 2,227,967 1/194'1 Favre 317 X 2,227,970 1/1941 Hill 317113 X 2,359,247 9/1944 Rowe 317120 2,530,945 11/ 1950 Chapman et a1 317--113 FOREIGN PATENTS 1,100,671 1/ 1968 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner D. SMITH, 1a., Assistant Examiner U.S. C1. X.R. 317- 101, 113 

